This study aimed to compare lung growth and development during the first year of life in healthy term infants of low or appropriate birth weight for gestation. Paired measurements of forced expiratory volume in 0.4 second, FVC, and forced expiratory flow when 75% of FVC has been exhaled were obtained, using the raised volume technique, at about 7 weeks and 9 months of age in 80 infants (32 low and 48 appropriate birth weight for gestation) of white, nonsmoking mothers. Forced flows and volumes increased with growth. Longitudinal trends in results were compared between the two groups, using random effects modeling and adjusted for potential confounding factors. After adjustment for sex, age, and length, forced expiratory volume was significantly reduced by an average (95% confidence interval) of 9% (2 to 16%) in low birth weight compared with appropriate birth weight for gestation infants throughout the first year of life, with a similar trend in forced expiratory flow (8% [-2 to 17%]) and FVC (4% [-3 to 11%]). These findings suggest that lung function is reduced in low birth weight for gestation infants born to nonsmoking white mothers and that this is independent of somatic growth during infancy.